The objective of this project is to develop methods to detect the rare expression of LDH-X, a sperm specific isozyme in single hepatocytes. The methods are to be used to measure possible changes in the frequency of LDH-X derepression that may result from exposure to environmental agents. Immunofluorescent techniques have been developed to detect LDH-X in mouse hepatocytes fixed on microscope slides. The frequency of hepatocytes reacting with anti LDH-X has been measured in male and female DBA/2J mice.